Process for converting petroleum hydrocarbons



Feb. 13, 1934. A. G. DAVIS PROCESS FOR CONVERTIG PETROLEUM HYDROCARBONS Filed Jan. 18, 1926 INVENTOR,

MEF/P7" 9. UAH/A5'.

A TORNEY.

Patented Feb. 13, 1934 STA'IESv PATENT OFFICE PROCESS FOR; CONVERTING rETRoLEUMf HYDRooARBoNs Delaware` Application January 18;

Claims,

This invention relatesL to, improvements`4 in. a process. for converting hydrocarbons, and refers more. particularly, to .a cracking processA in, whichA theoil, after. being convertedor cracked, ispassed 5 to-aseparatestage forfdistillationandin this,

stagel of. distillation or evaporation Vis introduced a relatively heavy` hydrocarbon, medulm. the character of this medium being such that sube stantially. none is volatilized.- or vaporized at the temperatures existing in the vaporizing stage. Suche. blending product wouldbe similar in its characteristics totheunvaporized or residual .ma-4 terial. withdrawn from thel vaporizing. stage and this.. product, it` hasl been found, isadmirably adapted-to be utilized as ablendingproduct.with. the,crackedhydrocarbons andis .used in ,amanner hereinafter.l described inmore detail.

The single feature is a` diagrammaticside ele-l vational view.y ofA apparatus. for. carrying out.. a

20. cracking process in whichthisiblendingv of, relativelyl heavy-material is employed by theintroduction,of theY blending oil tothe transfer line between. the reaction. stage; and, the vaporizing. stage, although it is,understoo.d thattheblending may. be elected by. introducing the blendingoil directly to-the evaporating stage.

Inthe-gure, at 1 is showna furnaceconsist.- ing; of: a^ combustionchamber. Zandacoil come. part-ment 3, in which. areV mounted. the pipecoils r 4. 'Ihe furnace'is preferably heatedbymeansofI gas` burnersA diagrammatically shown atA 5;. gas passing from thel combustion zone over the .tubes andout through the. flue 6` whichisconnectedto a chimneylor-stack. At.8 is shown anenlarged heavily insulated. forged steel reaction. chamber preferably. fabricated, from a. singleingotA and forged intoan elongated.v tube havingP bottle-neck ends.. Removable endplates are attached tox the ilangesy and` adapted.. to. be removed. forA the` pur- 407. poseot` cleaning. The chamber is mounted upQn suitable piers-shown at` 9. The dischargefrom thereaction chamber isy directly. connected by meansY of a transfer line, 10.` to, an evaporating towerll` which, inturn, is,connectedby, means of a` vapor. pipe 12, tov a.. dephlegmating, towerrpreferablv. of bubble.- typeconstruction-shown at 13, ThetopY of, the bubble tower has communication through a vapor line 14 with a coil 15 in the condenser boX 16, the discharge end of which, connects by means or" a pipe 17 tothe gas separator 18,.-the latter being equipped, with a gas Aoutlet 19` and a liquid draw oi line, 2 0, the lines 19 and 20 being; controlled by valvesV 2l, and 22,A respectively.` The liquid. level in the evaporator 1,1 is controlled by means of. a liquid level regulating 1926.'- Serial No. 81,915

device 23 manipulating the valve 24 positioned in theV draw 01T line 25. This draw off line terminatesin a coil 26 positionedin the cooling box2'7. This discharge from the cooling coil 26 is directed toY the accumulating tank 28 which is 60 equipped with two draw off lines 29 and 30, the former communicating witha storage receptacle not shown and the latter with the suctionl side of the pump3l. Each of the lines is equipped with a valve designated as 32 and 33, respectively.

The liquid level in the bubble tower or dephlegmator is controlled by means of a liquid level regulating device 34 manipulating the valve; 35 inthe draw off line 36 which has `communicationwitha returnline 37 connected to the suction 7o sideof the pump Y 3 A8V and a line 39. communicating with a storage receptacle not shown. The lines 3.7. 211.16.39 are controlled by valves 40.and 41, respectively.

Steamlines42 and 43 connect into the bottom 75 of thel evaporator 11 and the bubble tower 13l whereby steam may be introduced to the separate. stages in controlled quantities as desired.

Referring now to the operation of the process, the major stages of which follows the practiceA of. thecrossprocess, is as follows: f

Charging stock is introduced frornuany con, venient source throughthe line 44 and is charged by means of apurnp 45 through Va preheating coil 46-positioned inthe top of the evaporating tower 85 1 1. TheJ preheated oil isv then. directedthrough thevline` 47 to the` coils 4 positioned in the furnace 1. On its discharge fromthe heating coils 4,v the o il has reached aY cracking temperature but, conditions and velocity of theoilthrough the coils,A is so. regulated that. carbon deposition is substantially eliminated from the coils. From the heating coils the oil is directed to the reactionv chamber where it is collected in a considerable body and remains for a sufficient period of time to undergo adequate digestion, that.is, to complete the cracking reaction initiated in the heating coil. 'I The reaction chamber 8 is heavily insulated toprevent the loss of heat by radiation. The Chamber is equippedwith pressure recording gauge/18 to, facilitate the pressure control. Temperatures and pressures are regulated to effect the conversion of the oil while the same is maintained substantially in the liquid. phase or with! out substantial vaporization.

The ysynthetic crude or crackedY products are discharged from thereaction` chamber 8 through the transfer line l()A in which is interposed a pressure` reduction valve 49. rIhere is alsoA connected into thisy transfer line posterior to the 110 valve 49 a line connection 50 which communicates with the discharge from the pump 31. The cracked or synthetic products, in a highly heated condition and at high pressures, pass through the which the still volatile material passes off from` the top of the tower through the line 14 to the condenser 15 and finally into the gas separator 18.

The reflux material knocked back in the bubble tower is drawn off through the line 36 and recirculates back to the heating coil through the line 37 and pump 38 or it may be diverted from the system through the line 39. The bottoms withdrawn Vfrom the evaporator which Vcomprises a relatively heavy liquid hydrocarbon unvaporized at the temperature conditions existing in the evaporator, are drawn off through the line 25 controlled by a valve 24 and, after passing througha cooling coil 26, are collected in an accumulating or settling tank 28 from which tank they may be diverted to storage or returned by means of the pump 31 and charged into the vaporizing stage through the pipe 50 which communicates, as previously stated, with the transfer line 10. It is this recycling or the utilization of a relatively heavy liquid hydrocarbon which will not readily vaporize at the temperature conditions existing in the evaporator when used in a process of the type described, that forms the novelty of the invention as the practice described in connection with the main apparatus itself is an operation well known in the art. It is recognized that it is common practice to introduce a cool hydrocarbon to the evaporating stage to retard, to a certain extent, the evaporation taking place in the vaporizing stage, but it is thought novel to select a particular hydrocarbon having the characteristics hereinafter described in more detail for an operation of the type described and particularly the residual material withdrawn from the evaporating stage for circulation back into the system as the blending medium for the synthetic orcracked products discharged from the reaction stage into the evaporator. It is thought tc be new, also, to utilize a medium such as a residual product drawn oif from the evaporator as a blending oil with the synthetic crude or cracked products discharged from the reaction stage in a system wherein the synthetic products are passed, without cooling, from the reaction stage to an evaporating stage. Where the synthetic crude is discharged in a highly heated condition from the reaction stage, it is normal practice in the production of gasoline distillates directly from the system to partially cool the oil prior to vaporizing it, as otherwise excessive evaporation takes place, resulting in the distillation of certain of the objectionable high-boiling point products which tend to overload the reuxing and fractionating system beyond its capacity and, furthermore, producing an objectionable residual bottom in the evaporator such as a non-fluid residuinn or coke.

By utilizing the liquid bottom withdrawn from the evaporator, substantially none of such a cooling medium recycled through the pump 31 as described, is evaporated overhead from the evaporating stage as it has already been subjected to the temperature conditions existing in the evaporator. This is an important operating point as it cuts to a minimum the vapor to be carried over to the refluxing or fractionating system. In other words, no vapor is carried to the refluxing apparatus except the normal fractions of the synthetic or cracked products lighter than the residuum.

Furthermore,l the practice as described promotes the production of a lower percentage of residual products as the operator can control the gravity of the unvaporized products taken 0E from the evaporator at a lower point by this' method without the danger of advancing into the zone of operation wherein there is objectionable coke formation. This accuracy of control is important as it automatically increases the percentage of recharging stock produced as a somewhat deeper distillation cut can be made into the cracked product than where cooling is relied upon to prevent the passage overhead of too great an amount of these higher boiling point fractions. This increase in the percentage of recharging stock in turn shows a greater ultimate yield in the gasoline, as this yield is to a great extent dependent upon the percent of recycled stock.

The system has the further advantages that less fluctuation occurs in the temperature con- "f trol'of the evaporator than when using a charging stock as a blending medium. It has been found, under certain conditions, advantageous to introduce steam into the bottom of the evaporator through the line 42 by means of a perforated pipe in the bottom of the evaporating tower by means of which a better control is obtained on the flash point and the initial boiling point of the residual or unvaporized bottoms withdrawn from the evaporator. The utilization of these residual products, as previously described, permits the passing of the synthetic crude directly to the evaporator without rst passing the cracked products or synthetic crude through a cooling stage. It has been found of considerable advantage in operating a system of this type to introduce steam into the bottom of the bubble tower or dephlegmating column 13 to facilitate the evaporation of the reux material. This steam is introduced by means of the line 43 in quantities regulated according to the operating conditions existing in the tower.

This type of blending oil has the effect of preventing carbonization or carbon collection in the transfer line and assures the discontinuance of cracking at the point of pressure reduction'or prior to the introduction of the synthetic crude to the evaporator. Furthermore, it has the effect of producing a more uniform residual material ultimately withdrawn from the evaporating stage. The accumulating tank serves not only to maintain a constant ancladequate supply of the medium for circulation through the pump 3 1, but permits the residual material to collect in a stagnant pool wherein the free carbon particles will have ample opportunity to settle out. thereby relieving the system of accumulations in the active operating stages.

. I claim as my invention:

1. A. process of converting petroleum hydrocarbons, comprising the steps of subjecting the oil to cracking conditions of temperature and pressure in a heating stage, passing the oil to a digesting stage wherein it is maintained at a cracking temperature while under pressure,

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passing the cracked products to a zone of reduced pressure wherein the lighter fractions are distilled olf, introducing into the zone of reduced pressure a hydrocarbon medium substantially none of which will volatilize in the reduced pressure zone.

2. A process of converting petroleum hydrocarbons, comprising the steps of subjecting the oil to cracking conditions of temperature and pressure in a heating stage, passing the oil to a digesting stage wherein it is maintained at a cracking temperature while under pressure, passing the cracked products without cooling to a Zone of reduced pressure wherein the lighter fractions are distilled off, introducing into the zone of reduced pressure a hydrocarbon medium substantially none of which will volatilize in the reduced pressure zone.

3. A process of converting hydrocarbon oil comprising subjecting the oil to cracking conditions of temperature and pressure in a heating stage, passing the oil to a digesting stage wherein it is maintained at a cracking temperature while under pressure, passing the products of conversion to an evaporating stage maintained at a pressure materially lower than that in the digesting stage, distilling off the lighter fractions of the products of conversion, withdrawing the unvaporized products from the evaporating stage, cooling the unvaporized products and recycling them to the evaporating stage to check the cracking reaction.

4. A process of converting petroleum hydrocarbons, comprising the steps of subjecting the oil to cracking conditions of temperature and pressure in a heating stage, passing the oil to a digesting stage wherein it is maintained at a cracking temperature while under pressure, passing the cracked products to a zone of reduced pressure wherein the lighter fractions are distilled 01T, introducing into the zone of reduced pressure a hydrocarbon medium substantially none of which will volatilize in the reduced pressure Zone and introducing steam into the cracked products in the reduced pressure zone.

5. A process of converting petroleum hydrocarbons, comprising the steps of subjecting the oil to cracking conditions of temperature and pressure in a heating stage, passing the oil to a digesting stage wherein it is maintained at a cracking temperature while under pressure, passing the cracked products into an enlarged evaporating stage maintained under a relatively low pressure wherein the lighter fractions thereof are distilled off, fractionating said lighter fractions to condense and separate higher boiling constituents therefrom, withdrawing the unvaporzed products from the evaporating stage and returning the unvaporized products to the evaporating stage to check the reaction.

ALBERT G. DAVIS. 

